This invention relates to processes for the manufacture of plastic tube bundles useful for heat exchangers. More particularly, this invention relates to such processes incorporating polymer to affix such tubes into desired positions.
Many heat exchangers are constructed from tubes and tube sheets. Tube sheets are essentially flat sheets provided with holes to admit the tubes. In assembly of the heat exchanger, tubes are inserted into these holes and are then bonded to the tube sheet, by brazing or other methods in the case of metal cores, or by thermal bonding processes involving melting in the case of plastic cores. The process of inserting small diameter, thin wall plastic tubes into the holes of the tube sheet, also known as threading, can be mechanically demanding and can limit the rate of heat exchanger production and economic attractiveness.
Alternatively, in the case of plastic cores, the tube sheet can be formed by stacking a number of saddle-like layers. Each element is bonded to the adjacent element(s) by a thermal process such as vibration or ultrasonic welding. Such a process is described in EP 0 673 496 B1. While this process avoids the need for a threading step, the mechanical strength of the resulting tube sheet is limited by the number and quality of the individual bonds required to build the tube sheet.
It is an object of the present invention to provide a process for the fabrication of plastic tube bundles for heat exchangers which is adaptable to incorporate a variety of shapes of tubes. A feature of the present invention is the improved speed of fabrication of the heat exchanger assembly versus conventional techniques. It is an advantage of the present invention to provide a process that does not require acute positioning of the tubes prior to securing them together. These and other objects, features and advantages will become apparent upon having reference to the detailed description herein.
The present invention provides a process for fabricating a plastic tube bundle for a heat exchanger structure comprising:
providing a layer of polymeric tubes having a plurality of tubes held in proximity and side by side to each other,
pouring molten polymer over the tubes sufficient to embed the tubes therein,
positioning an additional layer of such tubes on the polymer while said polymer is still soft, so that the tubes are embedded in the layer,
pouring additional molten polymer over the additional layer of tubes,
repeating the last two steps at least once to form a bundle,
cooling said bundle to harden the polymer, and
fashioning the tube bundles including the ends of the tubes encased in said polymer to communicate with one or more headers to collect heat exchange fluid.